The present invention relates to machining and milling tools used to shape or dress material surfaces. More particularly, this invention relates to improved, replaceable cutter inserts supported in a ball nose end mill tool body for rotational cutting engagement with a work-piece material.
Milling cutters are commonly used in the machining industries for cutting or removing an undesirable portion of material from a work-piece to fabricate or form a desired shape in the remaining work-piece material. Milling cutters are typically either a one-piece with the tool body or use replaceable inserts mounted to the tool body. When worn or dull, one-piece cutters are either sharpened or discarded, and may be more economical for small size milling cutters than insert type cutters. Insert type cutters are commonly used in operations involving long production runs or in association with larger cutting tools, conserving the tool body for re-use. These cutter inserts take on a variety of shapes and forms as required to produce a desired cut in a work-piece. Depending upon their fabrication and use, the inserts may be disposable or may be resharpened for reuse. Inserts may be manufactured from hardened alloys, such as tungsten carbide, cast alloy, or high-speed steel. In some embodiments, the inserts may include carbide or cast alloy tips.
A ball nose end mill is a particular type of milling cutter having a radially curved cutting edge defined by a curved cutting face intersecting a curved land surface. From an axially leading tip of the insert, the cutting surface may curve into tangential engagement with one or more axially trailing straight cutting surfaces spaced apart from and axially parallel with a tool body rotational center axis. Ball nose end mills may initially create an axially directed force on the work piece, creating an axial bore in the work piece. As the bore is deepened, curved cutting areas are exposed to the deepening borehole. Ball nose end mills may be used for shaping or forming a cavity or making other cuts involving removing material in depth or bore penetration movement and/or lateral movement of the rotating ball nose end mill relative to the work-piece.
Cutter inserts may be removably affixed within a cutting end of a ball nose end mill tool body by a conventional securing member, such as a bolt. Cutter inserts for ball nose end mills may be flat-faced inserts positioned on opposite sides of the rotational center axis. Other single body inserts have a tip or leading cutting surface positioned substantially on the rotational center axis and have curved cutting surfaces extending from the tip cutting surface to respective sides of the tool body. Both the multiple insert embodiment and the single insert embodiment preferably provide two curved cutting edges. Each cutting edge may lie substantially within a plane, creating what is commonly known within the industry as a xe2x80x9cstraight flutexe2x80x9d cutting surface, as opposed to other shapes, such as xe2x80x9chelical flutes.xe2x80x9d Helical shaped blanks are impractical for insert type ball nose end mills because the relatively small size of the ball nose tool body does not provide sufficient material to adequately support a helical cutter insert. In larger sizes, the insert itself is both difficult to form and to support in the tool body. A ball nose end mill with a pair of replaceable cuter inserts is disclosed in U.S. Pat. No. 6,102,630.
Inserts for ball nose end mills with flat cutting face surfaces provide a poor cutting action because the cutting edge and flat face of the insert engage the work piece in a blunt fashion, as opposed to along a cutting edge. Thereby, there is substantially no axial or radial rake (shear angle) between the insert cutting edge and the work piece. The mill may tend to xe2x80x9cchatterxe2x80x9d or vibrate as it rotates in engagement with the work piece, which can be severe. Chatter may lead to increased milling time, shortened tool life, and milling equipment failure. Such vibration may also cause rough, uneven cuts in the work piece. A rotating ball nose end mill may be directed to move axially along the rotational center axis so that the front tip of the insert located on the rotational center axis engages the work piece. As the mill continues to move axially, the insert may bore into the work piece. As the mill continues to bore into the work piece, loading on the insert may spread radially outward along the cutting edge until the insert is engaged with the work piece across the full diameter of rotation. If the mill is moved laterally through the work piece, the mill may experience side loading upon the insert. Combinations or axial and lateral movement create a variety of load conditions upon the insert. For a rotating flat cutting face insert, any such movement undesirably results in blunt engagement with the work piece, without the benefit of radial or axial shear angles.
The disadvantages of the prior art are overcome by the present invention, and an improved cutter insert for a ball nose end mill is hereinafter disclosed.
The cutter insert of the present invention improves ball nose end mill cutting efficiency by providing a wavy or serrated cutting edge on the insert. The serrated edge may provide axial and radial rake to the cutting edge on an insert cutter. In one embodiment, the serrated surface is shaped in a sinudoidal or wavy pattern, having a repeating plurality of crests and roots along the cutter face. The tool body holding the cutter insert rotates the cutting face about a rotational center axis. Each segment or portion of the cutting face radially outward from the center axis of rotation rotates along a circular path. With the exception of the serration crests and roots, the sinusoidal pattern of the cutting edge positions each finite segment of the cutting edge at an angle with respect to the direction of rotational movement of the respective edge segment. Thereby, a plurality of shear angles may be provided over a substantial portion of the cutting edge (during rotational movement of the cutting face) as opposed to blunt engagement which may occur substantially at only points coinciding with the crest axis of the serration peak and the root axis of the serration root. The plurality of shear angles and/or rakes translates into improved cutting or shear along the cutting edge.
An additional cutting advantage may be obtained by a relief angle formed along the cutting edge, wherein the plane of the relief angle intersects the plurality of crest peaks and roots along the cutting face. Thereby, as a result of the relief angle and the serrated face pattern, each of the sinusoidal peaks may be a radial and/or axial leading cutter edge, while the sinusoidal roots may be a trailing cutter edge. The plurality of cutting edges between the each crest and adjacent root may form a corresponding plurality of axial rake angles with respect to the rotational direction of insert movement. Along the length of the cutting edge, the position and orientation of the cutting forces along the crests and roots, changes radially with respect to the distance to the centerline of rotation, as well as axially with respect to the centerline of rotation, and in angular orientation. The plurality of angles and radial positions along the length of the cutting edge translates into improved shear of the work piece along the cutting edge.
It is an object of the present invention to provide an improved ball nose end mill cutter creating a plurality of radial and/or axial rake angles in a straight flute cutter. A plurality of angles are provided along a cutter face by shaping the cutter face to include a plurality of serrations or wavy profiles having repeating crests and roots along the cutter face and cutter edge.
It is an additional object of the present invention to provide a removable cutter insert including the serrated cutting edge for a ball nose end mill. Although the serrated cutting edge may be formed in the cutting end of a single body milling tool, a preferred embodiment provides replaceable inserts providing the serrated cutting edge.
It is a feature of the present invention that the improved cutter inserts may be formed for removable affixation within existing ball nose end mill tool bodies.
It is yet another feature of this invention that the improved cutter insert may be provided with a grooved contact surface for interlocking engagement with a tool body possessing mating engagement grooves therein, to rigidly secure the insert within the tool body.
Still another feature of the present invention is that the improved cutter may be provided as a single insert including opposing cutting edges, frequently desired for a rotational ball nose end mill use. Thereby, cutting edges may be provided on each side of a common cutter insert.
It is an additional feature that the improved cutter may be provided as two or more separate cutter inserts for simultaneous engagement with a tool body.
It is an advantage of the present invention that the cutter inserts may be provided with a variety of selected serration patterns and dimensions, including particular relief angles, crest to root heights.
A further advantage of this invention is that the cutters may be manufactured from carbide, cast alloy, diamond impregnated, or high speed steel materials.
These and other objects, features, and advantages of the present invention will become apparent and will become more fully described and appreciated from the following claims and detailed description, wherein reference is made to the figures in the accompanying drawings.